1. Field of the Invention
This invention relates in general to a semiconductor manufacturing process, and more particularly to a method of forming a conductive plug to avoid voids.
2. Description of Related Art
When the density of the integrated circuits increases, the surface of a chip might not provide enough area for interconnects to lay thereon. For the need of interconnects with reduced size of metal-oxide-semiconductor transistors, more than two metal layers become the necessary way for many integrated circuits. For some complicated products, such as microprocessors, even more metal layers are needed to complete the interconnection between individual devices within the microprocessor. Different metal layers are connected by conductive plugs.
Usually, a conductive plug is formed by etching an insulating layer to form a contact hole, then filling a conductive material such as tungsten into the contact hole. Because the adhension between the conductive material and the insulating layer is defficient, a glue/barrier material must be formed between the conductive material and the insulating layer. Commonly used glue/barrier materials include Ti, TiN.sub.x or TiW formed by physical vapor deposition (PVD) or chemical vapor deposition (CVD).
However, the conductive plug of an integrated circuit formed by a conventional process is apt to generate voids. For more clearly understanding the reason, an example is used to explain the conventional process of fabricating the conductive plug of an integrated circuit.
FIG. 1 shows a cross-sectional diagram of a conductive plug of an integrated circuit formed by a conventional manufacturing method. An insulating layer 12, such as borophosphosilicate glass (BPSG) or oxide, is formed on the silicon substrate 10 or on a metal line. After, a portion of the insulating layer 12 is removed by etching to form a contact window 13 which exposes a region 10a of the conductive material by, for example, an anisotropic etching. A diffusion barrier layer 14 is formed on the region 10a of the conductive material and the periphery of the contact window 13, and extended to the upper surface of the insulating layer 12. The diffusion barrier layer 14 can be, for example, a TiN.sub.x layer which prevents diffusion and improves adhension. Then, a conductive material 16, for example, a tungsten, copper or aluminum, is filled into the contact window 13, by PVD or CVD. Since the step coverage is bad, a void 18 is formed therein.
In the above mentioned manufacturing method of the conductive plug of the integrated circuit, a diffusion barrier layer is deposited before the conductive material is filled into the contact window of the insulating layer as a glue/barrier layer. Therefore, the contact window becomes narrower, and deposition sites on the diffusion barrier layer become recessed, which results in voids generating when the conductive material is deposited. As a result, the large voids seriously affect the characteristics of the device such as resistance raising and short circuit.